Attempt at Maybe in Ruby

Maybe.rb

class Maybe
    def self.empty
        Maybe.new nil
    end
    def initialize(value)
        @value = value
    end
    def bind(f)
        @value.nil? ? self : f.call(@value)
    end
    def fmap(f)
        @value.nil? ? self : Maybe.new(f.call(@value))
    end
    def to_s
        @value.nil? ? "Nothing" : "Just #{@value}"
    end
    def value_or(x)
        @value.nil? ? x : @value
    end
end